Shit ninja as in the person we've only seen in the school in 2019 (iirc)? I guess the next question would be is shit ninja darci 2 (the one we see kill the scientist)? Or is there a random person who saved Jenny and then 20 years later appeared in front of all the 2019 high schoolers for a second? I think it being someone we've seen in both 2019 and 99 (dont think they aged 20 years naturally becuase they are still pretty "ninja" but i guess that could be porn/game logic) runs into alot of the same paradoxical issuesAnother example would be that the shit ninja saves Darci's mom solo, but with MC and Darci on the hunt for her they wind up doing much of the saving instead. The end result is the same but they get incorporated into the actual events.
What about the "original" timeline (before any time travel occurs) ? Or does this theory assume that the "very 1st time" 1999 happened there was already time travel from a point in a future despite the machine not being fully functional yet?